Electronically operated remote control systems, such as garage door openers, home security systems, home lighting systems, etc. are becoming increasingly common. Such electronic remote control systems typically employ a battery powered portable RF transmitter for transmitting a modulated and encoded RF signal to a receiver located at the remote control system. For example, a garage door opener system may include a receiver located within a home owner's garage. The garage door receiver is tuned to the frequency of its associated portable RF transmitter and demodulates a predetermined code programmed into both the portable transmitter and receiver for operating the garage door.
As an alternative to a portable transmitter, a trainable transceiver (e.g., a remote control transceiver) may be provided in vehicles for use with remote control devices such as garage door openers, gate controllers, alarm controls, home lighting systems, or other remotely controlled devices. FIG. 1 shows a vehicle 10 including a trainable transceiver used to control a remote control system 14. The transceiver (not shown) is mounted within the vehicle 10, inside, for example, a rearview mirror 16. The transceiver learns and stores the modulation scheme (i.e., code format), transmission codes and the particular RF carrier frequency of an OEM (original equipment manufacturer) remote transmitter 12 for use with the remote control system 14. The transceiver is trained using an original remote RF transmitter 12 for the remote control system. The coded RF (or infrared) energy of the transmitter 12 is transmitted as indicated by arrow A to the transceiver mounted in the rearview mirror 16 of vehicle 10. The transceiver receives the encoded transmitted energy, demodulates it and identifies and stores the control code and carrier frequency of the transmitted energy. Once trained to the control code and frequency of the remote transmitter 12, the transceiver can be used to selectively transmit coded RF energy as indicated by arrow T to the remote control system 14 that is responsive to the signal.
To enhance security of remote control devices, many manufacturers have implemented rolling code or cryptographic algorithms in their remote control system original transmitters and receivers to transmit and respond to randomly varying codes. A cryptographic algorithm is used to generate and encrypt a new control code for each transmission of the control signal. Typically, to keep track of which code is to be transmitted or received next, sequential code serial numbers are stored that identify which code was transmitted or received last, such that the next code will have associated therewith the next sequential serial number. To enable a vehicle-installed trainable transceiver to effectively operate in such systems, trainable transceivers have been developed that have the capability of recognizing when a received signal has been originated from a transmitter that generates a code that varies with each transmission in accordance with a cryptographic protocol. When such a variable code is recognized, the trainable transceiver determines which cryptographic protocol or algorithm is used to generate and transmit the next code to which the receiver will respond. Typically the receiver of the remote control system also needs to be trained to recognize and accept the transmitter as a valid transmitter for the remote control system (e.g., the receiver may be trained to recognize a unique transmitter serial number associated with the transmitter as valid). In addition, the receiver and transmitter are typically synchronized to a counter that increments or changes in a predictable way with each button press. The training of the receiver of the remote control system is commonly referred to as the second part of the training process or receiver training. An example of a trainable transceiver configured to learn variable codes as well as methods for synchronizing rolling codes are described in U.S. Pat. No. 5,661,804 herein incorporated by reference.